West Nile is a virus most commonly spread to people
by mosquito bites. In North America, cases of West Nile virus (WNV)
occur during mosquito season, which starts in the spring/summer and
continues through fall. WNV cases have been reported in all of the
continental United States, including Los Angeles County.

How do people
get infected with WNV?

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Mosquito Bites:
West Nile virus is most commonly spread to people by the bite of an
infected mosquito. Mosquitoes become infected when they feed on
infected birds. Infected mosquitoes then spread West Nile virus to
people and other animals by biting them.

In a very small number of cases, West Nile virus has been spread
through:
• Exposure in a laboratory setting
• Blood transfusion and organ donation
• Mother to baby, during pregnancy, delivery, or breast feeding

West Nile virus is not spread:
• Through coughing, sneezing, or touching
• By touching live animals
• From handling live or dead infected birds. Avoid bare-handed
contact when handling any dead animal. If you are disposing of a
dead bird, use gloves or double plastic bags to place the carcass in
a garbage can.
• Through eating infected birds or animals. Always follow
instructions for fully cooking meat from either birds or mammals.

Who is at risk
for infection with WNV?

Anyone bitten by a mosquito in an
area where the virus is circulating can get infected with WNV. The
risk is highest for persons who engage in outdoor work and
recreational activities. Elderly persons are at increased risk of
severe disease if they are infected.

How soon do
people get sick after getting bitten by an infected mosquito?

It takes 2-14 days after the bite
of an infected mosquito to develop symptoms of WNV.

What are the symptoms
of WNV?

No symptoms in most people. Most
people (8 out of 10) infected with West Nile virus do not develop
any symptoms.

Febrile illness (fever) in some people. About 1 in 5 people
who are infected develop a fever with other symptoms such as
headache, body aches, joint pains, vomiting, diarrhea, or rash. Most
people with this type of West Nile virus disease recover completely,
but fatigue and weakness can last for weeks or months.

Serious symptoms in a few people. About 1 in 150 people who
are infected develop a severe illness affecting the central nervous
system such as encephalitis (inflammation of the brain) or
meningitis (inflammation of the membranes that surround the brain
and spinal cord).
• Symptoms of severe illness include high fever, headache, neck
stiffness, stupor, disorientation, coma, tremors, convulsions,
muscle weakness, vision loss, numbness and paralysis.
• Severe illness can occur in people of any age; however, people
over 60 years of age are at greater risk. People with certain
medical conditions, such as cancer, diabetes, hypertension, kidney
disease, and people who have received organ transplants, are also at
greater risk.
• Recovery from severe illness might take several weeks or months.
Some effects to the central nervous system might be permanent.
• About 1 out of 10 people who develop severe illness affecting the
central nervous system die.

What should I
do if I think a family member or pet might have a mosquito-borne
disease?